Floor conveyors for use in automotive assembly plants are disclosed in Japanese Patent Publication No. 40145/1980 and U.S. Pat. No. 4,408,540. Such structures are not satisfactory for use in assembly plants.
In Japanese Patent Publication No. 40145/1980, the conveyor is mounted in a housing which is laid on top of the floor surface in the assembly plant which therefore provides a barrier to the movement of other objects across the conveyor line. The top opening of the housing is covered by a rubber or other elastic material for preventing entry of coating material into the housing. However, if an operator must cross over the conveyor, he cannot step on the rubber cover and it is also dangerous to straddle the housing. Such arrangement therefore restricts the ability of the operators to pass from one side to the other of the conveyor and thereby causes a reduction in work efficiency.
Even though the top opening of the housing is covered by the elastic material, when the conveyor operates to move the automobile body past the painting operation, the support leg for the automotive body must pass through the cover material which creates a spacing adjacent the support which may permit coating material to enter within the housing.
The automobile body is mounted on a carrier which travels along the rail, and to limit swaying of the body the carrier is provided with front, rear, right and left (i.e, four) guide rollers. On straight sections this is no problem, but going around curves or up slopes there must be sufficient clearance to permit the turning movement and it is possible that the rollers will derail.
The conveyor shown in U.S. Pat. No. 4,408,540 eliminates the enlarged upper opening which is characteristic of the Japanese patent and provides a narrow opening between closely-spaced rails. If the conveyor mounts an object such as a vehicular body having a large width (normally 1.5-2.0 meters) or another object whose center of gravity may be offset to one side owing to the presence of the steering wheel or the like, it is possible that the center of gravity of the body fails outside of the path of the carriers, and the carrier tends to tilt, even though guide rollers may be positioned between the traveling rollers. Even if the center of gravity of the body is normally directly over the rail, it is subject to swaying by reason of any small force which may occur in the normal handling operations involved in working on the automotive body. Swaying movement of the body on the conveyor is particularly serious when operations are being performed on both sides of the body at the same time. For this reason, the conveyor shown in the U.S. patent has not proved satisfactory.
The effect of swaying of the vehicular body will be described more concretely with reference to FIG. 11 of the attached drawings. In this figure, the automotive body M is shown supported on a stand mounted on a carrier between rails R. In the full-line position, the center of gravity of the body is directly over the center line of the rails. When a force f is applied to the right side of the body M, it sways to the position shown in broken lines in the figure.
If the height from a horizontally central surface H of the rails R to a point where the manual pushing force (f) is applied to a vehicular body M is L, a moment of inclination in a manual operation is fL. If the weight of the vehicular body is W, and an outside spacing between carrier rollers is (s.sub.1), a moment of stability resisting the moment of inclination is 1/2(Ws.sub.1). Therefore, when the moment of inclination fL is FL&gt;1/2 (Ws.sub.1), the vehicular body W is inclined by the manual pushing force. For example, if the height L, outside spacing (s.sub.1) and load W of the vehicular body are L=1,500 mm, (s.sub.1)=100 mm, and W=200 kg, respectively, the manual pushing force (f) is (f)&gt;6.7 kg. This magnitude of the force (f) does not allow the traveling rollers to be moved laterally relative to the rail R, and it will be appreciated that the vehicular body may be easily inclined or swayed by the manual pushing force. In the event that the center of gravity of the vehicular body is deflected, the vehicular body may be inclined even by further smaller force (f). Further, if a vertical spacing (d) between an inner surface of the rail R and the traveling rollers is d=3 mm, an amount of inclination during swaying of the vehicular body at the manually pushing point is 3.times.1,500/100=4.5 mm.
In other words, the vehicular body is likely to be inclined by its deflection of the center of gravity or an external force, and is inclined by a centrifugal force at curvature. For these reasons, there occur many problems which create a bad influence on the life of the rail, difficulty in manual operation, and reduction in quality, e.g. in painting, the painted surface is waved because of the swaying of the vehicular body upon passing through a connection of the rail. Consequently, this prior art conveyor is not satisfactory.